WASHINGTON—The Environmental Protection Agency launched a major new ad campaign Monday encouraging people to conserve resources by turning off their showers when they’re not showering. “We estimate that Americans waste up to 20 billion gallons of water each week by leaving their bathrooms with the shower still on, heading off to a full day’s work followed by a full night’s sleep, and then waking up the next morning to step into an already running shower,” administrator Lisa P. Jackson said of the EPA’s advertising effort, which includes TV spots that touts the benefits of turning showers off, such as not having a steamed-over bathroom mirror and not running out of hot water. “Nobody likes the inconvenience of having to manipulate a faucet first thing in the morning, of course, but we want to show people how the pluses of not leaving the water running all the time really can outweigh the negatives.” If the ads are a success, the EPA plans to launch a follow-up campaign in the spring urging people to conserve fuel by turning off their car engines when they return home for the night.